Antibiotics are substances that have typical ability to restrict microbes by different modalities.
One among them is through restricting the activity of RNA polymerase enzyme. The RNA polymerase enzyme is different in its structure, for prokaryotes and eukaryotes.
The particular feature of the enzyme to form a basic criterion is selective restriction of the activity of prokaryotic RNA polymerase. This is because it does not have any effect on the eukaryotic system in which the microbes reside upon.
Therefore, this is the reason why antibiotics specific in their action against prokaryotic RNA polymerase are highly successful.